Gas turbines generally include a compressor, one or more combustors, a fuel injection system and a multi-stage turbine section. Typically, the compressor pressurizes inlet air which is then turned in direction or reverse-flowed to the combustors where it is used to cool the combustors and also to provide air to the combustion process. In some multi-combustor turbines, the combustors themselves are located in a circular arrangement about the turbine rotor, in what is generally referred to as a “can-annular” array, and transition ducts deliver combustion gases from each of the combustors to the first stage of the turbine section.
More specifically, in a typical gas turbine configuration, each combustor includes a generally cylindrical combustor casing secured to the turbine casing. Each combustor also includes a flow sleeve and a combustor liner substantially concentrically arranged within the flow sleeve. Both the flow sleeve and combustor liner extend between a double-walled transition duct at their downstream or aft ends, and a combustor liner cap assembly at their upstream or forward ends. The outer wall of the transition duct and a portion of the flow sleeve are provided with an arrangement of cooling air supply holes over a substantial portion of their respective surfaces, thereby permitting compressor air to enter the radial space between the inner and outer walls of the transition piece and between the combustor liner and the flow sleeve, and to be reverse-flowed to the upstream portion of the combustor where the airflow is again reversed to flow through the cap assembly and into the combustion chamber within the combustor liner. Dry low NOx (DLN) gas turbines typically utilize dual-fuel combustors that have both liquid and gas fuel capability. One common arrangement includes five dual-fuel nozzles surrounding a center dual-fuel nozzle, arranged to supply fuel and air to the combustion chamber.
At various operating conditions, however, and in order to attain a high efficiency, it is desirable to maintain relatively high combustion gas temperatures for introduction into the turbine first stage. However, maintaining combustion gas temperatures at the desired high level will often negatively impact the service life of the hot gas path components subjected to such high temperatures.